...APRIL 29 2012...Caribbean Sea tropical disturbance emerges over the Florida Straits while upper-level winds quickly become more conducive for tropical development. Surface observations from south Florida show no signs of development at this time...but full birdseye discussions will resume immediately if this changes. This discussion supercedes full update #9 which had discounted potential for tropical development.

The special feature section of full update #9 mentioned the disturbance over the last several hours transitioning to a more subtropical state while supported by divergence E of the cut-off upper trough axis located over the E Gulf of Mexico/Yucatan. It was also mentioned that CIMSS products from University of Wisconsin showed a decrease in the southerly vertical shear associated with calm upper winds near the upper trough axis. However...tropical/subtropical development was discounted in full discussion #9 as the computer models showed an eventual de-amplification of the upper trough...which would have re-increased the vertical shear and reduced the supportive divergence east of the upper trough axis.

Figure 1 below instead shows what has happened to the upper trough between full discussion #9 (181Z Apr 28) and this special update #9A (1315Z Apr 29). The thunderstorms have gained great concentration to the NE of the upper trough axis...resulting in a new warm core upper ridge axis and associated cirrus outflow (which also suggests a trend from subtropical back to a more tropical state). In turn...this new upper ridge axis has caused the upper trough definition to become much more amplified by 1315Z today...to the degree that there is even a new cut-off upper low just N of W Cuba! The NW to SE tilting of the amplifying upper trough has changed the upper wind direction over the Florida Straits to a more easterly direction...which is reducing the vertical shear as the upper winds become more aligned with low-level easterly trade winds. The sharpening upper trough has also increased the divergence over the Florida Straits...and a surface trough has formed as a result as of 0600Z TAFB (kudos to the GFS model which had predicted this would happen as of full discussion #9).

The fate of this disturbance still will be associated with how this upper trough evolves. First off...radar imagery from S Florida (Figure 2) shows a spin developing SE of Key Largo. An isolated rain band moving SW suggests another possible spin due S of the Florida peninsula. This could mean the new 0600Z TAFB surface trough is developing a closed circulation supported by the divergence of the upper trough. Observations in S Florida at this time do not support this theory with stiff surface easterly winds across the board and surface pressures remaining steady at a high 1017 mb. When compared with Figure 1...the GFS computer model is initialized with an under-represented amplitude of the recently-sharpened upper trough. However...the GFS model has the upper trough getting even sharper thru 2100Z today. The GFS then gradually de-amplifies the upper trough while moving it east into Florida tomorrow April 30...and then dissipates the upper trough altogether by May 1. This means westerly vertical shear should re-increase and the favorable upper divergence reduce. This is why I am still iffy on tropical development as the window of favorable upper winds should last only today according to the models. However..one has to be a bit skeptical of the models as they did not predict today's dramatic amplification of the upper trough described in the third paragraph of this update. If surface observations from Florida or elsewhere indicate surface pressure drops and a developing closed circulation...then I will be resuming full birdseye discussions. Otherwise...this is my last discussion until hurricane season starts June 1 2012.

In lieu of these updates...I have to update the rainfall forecast from previous full discussion #9. The 200 mb GFS run has the upper trough getting even sharper thru 2100Z today...and then gradually dissipates the upper trough while moving it east thru May 1. The 850 mb GFS model run has the Florida Straits surface trough turn westward into the south-central Gulf of Mexico (while steered by the low-level ridge axis due N) and dissipates it May 2 (since the supporting upper trough is dissipated by May 1). So does the rainfall move east while supported by the divergence of the dissipating upper trough? Or does the rainfall move west while associated with surface convergence of the surface trough? I'll go with something in the middle...and say the rainfall will be largely stationary and gradually weakening with both the surface and upper troughs dissipating by May 1 and 2.

Steady heavy rainfall/flooding potential in the west Bahamas/S Florida will persist south of the red line in Figure 2 (line running from West Palm Beach to Belle Glade to Naples). Rainfall to the north of this line will be largely limited. Some of the rain shield may expand northward beyond the red line only if the thunderstorm mass expands in size under the supportive upper ridge axis outflow shown in Figure 1.

The Florida Keys may not see as much rain. Right now the Keys are in a dry slot to the SW of the radar rotations in Figure 2. They will be entering the rain mass NE of the rotations once the rotations travel westward. However...it is entirely possible the Keys never escape the dry slot...which is induced by upper-level convergence on the back side of the upper trough. With the models suggesting the upper trough moving eastward...the dry slot may follow suit and expand northeastward. If this dry air mass indeed expands northeastward...it will also begin to end the rainfall from south to north on the mainland of S Florida.

...SPECIAL FEATURE...CARIBBEAN SEA DISTURBANCE...The disturbance over the last 24 hours has transitioned to a more subtropical state. Instead of being supported by outflow beneath the warm core upper ridge displaced to the east (as in a tropical system)...the thunderstorms have gained greater concentration toward western Cuba and the Cayman Islands while now supported by divergence east of the cut-off upper trough axis located over the E Gulf of Mexico/Yucatan.

CIMSS products from University of Wisconsin show a decrease in the southerly vertical shear levels in a narrow swath along the E Yucatan shore associated with calm upper winds near the upper trough axis. But also... the upper trough axis has brought in dry air from the west which had been generated by convergence west of the upper trough axis. This dry air is why there is a distinct absence in thunderstorms in the NW Caribbean Sea.

With this disturbance now more supported by divergence E of the upper trough axis...the fate of it will be associated with how this upper trough evolves. First off...the TAFB analyses have dropped all surface troughs supported by the upper trough...suggesting insufficient divergence to support surface pressure drops. The GFS model however redevelops a surface trough in the Florida Straits. But also...the models de-amplify the upper trough and move it east which will increase westerly vertical shear and reduce the supportive divergence east of the upper trough axis...and no subtropical/tropical development will occur as a result. The GFS model eventually dissipates its Florida Straits surface trough while it moves west into the Gulf of Mexico while steered by the surface ridge due north.

As for the rainfall...the past 24 hours have seen the thunderstorms concentrate more westward over the Cayman Islands...west Cuba..the western Bahamas...and SE Florida while becoming more associated with divergence E of the upper trough axis. Based on the models drifting the upper trough eastward and de-amplifying it...I expect this rain mass to gradually shift east and weaken.

...NORTH AMERICA DISCUSSION...The 997 mb extratropical cyclone over E Maine has intensified to 982 mb and moved northward into the east coast of Ontario. Strong southward cold air advection behind the intensifying cyclone has amplified its supporting upper trough into an upper low vortex now just SW of the 982 mb center. The 982 mb cyclone has absorbed what was a 1003 mb cyclone in north-central Ontario 24 hours ago.

The western US upper trough mentioned in the previous discussion has become cut-off into an upper low vortex over the W Dakotas...to the south of a Manitoba upper ridge in the westerlies. Computer models re-link the cut-off upper low vortex with the westerlies while merging it with the next upper trough in the westerlies. Meanwhile the surface cyclone supported by this upper disturbance has weakened and moved NW while steered around the cut-off upper low vortex. The main center of this cyclone is 1006 mb over SW North Dakota. The cold front once attached to this cyclone has a 1005 mb center over S Oklahoma...1011 mb center over Missouri/Illinois border...and 1015 mb center over E Kentucky.

Convergence E of the aforementioned Manitoba upper ridge supports a strong surface ridge of 1030 mb just SW of Hudson Bay and another surface ridge center of 1028 mb near E Michigan.

...DISCUSSION OF OPEN ATLANTIC WATERS...The cold front mentioned in the previous discussion...running from Greenland to the waters E of Bermuda and N of Puerto Rico...has mostly dissipated with the exception of a segment marked toward the NE corner of the above charts. The position of this remnant segment is based on an eastward moving cloud band in satellite imagery. The upper trough associated with the diminished cold front has fractured into one upper trough axis NW of the Azores and another upper trough axis to the SW of the Azores. Divergence from the upper trough SW of the Azores is supporting cloudiness well S of the Azores and SW of the Canary Islands.

Surface trough located midway between the Cape Verde Islands and Lesser Antilles continues westward while steered by the greater-than-1028 mb surface ridge NW of the Azores. It continues to be inactive while beneath convergent upper-level NW flow.

Amplified upper trough in the E Atlantic continues. The NW Africa/W Europe cold front supported by its eastern divergence is now barely within the scope of the above charts as of 1800Z TAFB. Its divergence has also has generated a surface trough also marked in the above charts running from near the Azores to Portugal. Convergent upper-level NW flow west of this upper trough axis continues to support the greater-than-1028 mb surface ridge NW of the Azores.

2012 Atlantic Hurricane Season Birdseye Discussion #8

...APRIL 27 2012...Central Caribbean Sea tropical disuturbance mentioned in special discusison #7B not expected to develop into a tropical cyclone. However I am resuming full birsdeye discussions in case this changes.

This is the eighth birdseye discussion of the 2012 Atlantic Hurricane Season. See previous discussion #3 concerning the idea behind this new type of discussion forum.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1925Z-released HPC analysis.

...SPECIAL FEATURE...CENTRAL CARIBBEAN DISTURBANCE...In previous full discussion #7...specifically the North America discussion...there was mention of a NW US frontal system with a 1003 mb cyclone over the W Great Lakes that had merged with a central US upper trough. This system eventually moved into the eastern US and triggered an unusually late winter storm (extratropical cyclone) that dumped heavy snow in western New York State and Pennsylvania.

Since then, the associated large upper trough and surface cold front of this winter storm emerged into the western Atlantic. Showers and thunderstorms have greatly increasing across the central Caribbean Sea over the last days as the upper trough/surface cold front interacted with the surface South American monsoon/ITCZ.

Latent heat release continues with these thunderstorms...and the upper flow has responded with warm core upper ridging developing overhead. However...the former winter storm upper trough left a fracture behind in the eastern Gulf of Mexico/Yucatan (marked in above charts)...and this upper trough fracture has maintained strong southerly shear across the disturbance and kept the warm core upper ridge displaced to the east. I do not ever expect tropical cyclone formation with too much vertical shear in the region.

Regardless of tropical cyclone development or not...impacts have been persistent...with the upper southerly flow transporting moisture from this disturbance northward...bringing prolonged rains/flooding potential to Jamaica...Cuba...Haiti...the Dominican Republic...the Cayman Islands...and the Bahamas.

...NORTH AMERICA AND ATLANTIC WATERS WEST OF 40W LONGITUDE...The above special feature discussion mentioned a strong winter storm (extratropical cyclone) that dumped snow earlier in the week in western New York and Pennsylvania. Even today...remnant features of this winter storm remain well-within the above charts. The winter storm barreled northward into Hudson Bay...made a cyclonic loop beneath its parent upper trough...and now has shifted eastward and is a shadow of its former self as a 1003 mb low in north-central Ontario in the above charts. The parent upper trough that once supported it has shifted east into the north-central Atlantic to the south of Greenland and now supports the ex-winter storm's original cold front. This original cold front extends far south into the Atlantic waters east of Bermuda and N of Puerto Rico. Finally...the ex-winter storm left behind an upper trough fracture in the east Gulf of Mexico/Yucatan as mentioned in the above Special Feature discussion.

While the winter storm was making its cyclonic loop over Hudson Bay...an upstream mid-latitude extratropical cyclone and its upper trough snuck in to its south. This extratropical cyclone is now 997 mb over E Maine and this upper trough is over Hudson Bay-to-Massachusetts. Divergence east of this upper trough now supports thie 997 mb cyclone and also the above mentioned ex-winter storm 1003 mb cyclone over north-central Ontario.

A feature that is entering the scope of the above charts is a western US sharp upper trough and equally vigorous surface cyclone. The surface cyclone has a 996 mb center over western Kansas...999 mb center over Colorado...and finally a 997 mb center over NE Wyoming as of 1925Z-released HPC analysis.

...ATLANTIC WATERS EAST OF 40W LONGITUDE...Ahead of the NE US winter storm over the past week was immense warm air advection that has developed an upper ridge axis presently stretching from Newfoundland all the way south to the Lesser Antilles.

As this upper ridge amplified...so did a downstream upper trough in the E Atlantic which is still very well-defined in the above charts. This E Atlantic upper trough contains some of the remnant vorticity of last week's Invest 91-L parent upper low. This upper trough's eastern divergence supports a cold front that has pushed southward from W Europe into NW Africa. A well-organized comma-shaped cloud mass SW of the Canary Islands is associated with an upper low vortex that has spun up along the upper trough in the last 24 hours. This upper trough's eastern divergence also generated a new surface trough in this vicinity also 24 hours ago that has since migrated west under the steering of a greater-than-1028 mb ridge NW of the Azores. This surface trough is now midway between the Cape Verde Islands and Lesser Antilles and inactive while now beneath upper-level NW flow convergence west of the upper trough.

The aforementioned greater-than-1028 mb surface ridge NW of the Azores is supported by upper-level NW flow convergence west of the E Atlantic upper trough.

...APRIL 26 2012...This partial discussion is issued as a special update concerning a potential tropical disturbance developing in the central Caribbean Sea.

During the previous week, an unusually late winter storm extratropical cyclone dumped heavy snow in western New York State and Pennsylvania. Since then, the associated large upper trough and associated surface cold front has emerged into the western Atlantic. Showers and thunderstorms have been gradually increasing across the central Caribbean Sea as the upper trough/surface cold front interacts with the surface North South American monsoon/ITCZ.

Upper-level flow is both southwesterly and divergent in advance of the large upper trough. The divergent aspect of the upper flow...coupled with surface convergence from the surface cold front & ITCZ/north South American monsoon...are repsonsible for the activity presently in the central Caribbean. The southwesterly aspect of the upper flow is shearing the disturbance. However if latent heat release continues with these thunderstorms...the upper flow could become more anticyclonic as a warm core upper ridge develops overhead. If this were to occur...this would enhance the outflow and reduce the vertical shear...and a tropical disturbance would be very likely. Should this happen...I will be re-issuing full birdseye discussions.

In the short term...expect the upper southwesterly flow to transport moisture from this disturbance northeastward...bringing rains to Jamaica...eastern Cuba...Haiti...and the Dominican Republic.

...APRIL 19 2012...This partial discussion is issued as a special update concerning special feature Invest 91-L mentioned in previous full discussion #7.

The parent upper low over 91-L has been shifting northward througout the day as it becomes increasingly gravitated toward a central US upper trough approaching from the west. The surface low of 91-L began tracking eastward last evening while steered by the south side of the upper low and was expected to soon turn northward while entering the east side of the upper low. The northward turn of the surface low will now be delayed due to the northward shift of the parent upper low. This is because the surface low will be embedded in vast steering westerlies south of the upper low. The prolonging of the surface low's eastward track give its more time before it will be absorbed by the cold front of the incoming central US upper trough.

Despite more time till absorption...Invest 91-L is no longer a risk of subtropical cyclone formation as the surface low of Invest 91-L no longer has bursts of convection. The loss of convection perhaps is also attributed to the northward shift of the parent upper low. The coldest temps of the upper low center have moved away from the surface low as the upper low shifted northward. This upper-level cold air was crucial in de-stabilizing the atmosphere of the surface low...which is tracking over mild water temps of 20 to 21 deg C and needs upper-level cold air to produce convection at those water temps. The loss of convection may also be attributed to dry air ingestion of neighboring dry air S of Bermuda mentioned in discussion #7.

With 91-L not expected to develop into a subtropical cyclone, this is the last birdseye Atlantic discussion until Atlantic Hurricane Season starts June 1 2012.

2012 Atlantic Hurricane Season Birdseye Discussion #7

...APRIL 18 2012...Invest 91-L running out of time to become a subtropical cyclone. This could be the final full discussion until hurricane season starts June 1 2012 (see today's special feature section below for details).

Invest 91-L has been moved from the Open Atlantic Waters discussion (where it has been mentioned in the last days) to its own special features section. This has been at the request of fellow blogger "KoritheMan." From now on each area of disturbed weather that is deemed a threat for tropical development on this blog will get its own special features section. All active tropical/subtropical cyclones will each get their own special features section as well. Of course this will add a challenge as what I deem a threat for tropical development may/may not align with the opinion from the National Hurricane Center and other fellow bloggers.

This is the seventh birdseye discussion of the 2012 Atlantic Hurricane Season. See previous discussion #3 concerning the idea behind this new type of discussion forum.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1916Z-released HPC analysis.

...SPECIAL FEATURE INVEST 91-L...Hot topic continues to be surface low Invest 91-L east of Bermuda, which has weakened from 1002 mb to 1006 mb over 24 hours as it struggles in what is a non-divergent environment beneath its parent upper low. The long-awaited SW track into 20 to 21 deg C waters has finally occured, which was anticipated in the last two discussions of this feature. Yesterday's discussion of this feature was at a climax...waiting to see if persistent convective cloud tops were to develop when this low arrived to those waters. It was concluded that if convective cloud tops did not develop, the parent upper low above was not cold enough to de-stablize the atmosphere at those water temps and subtropical cyclone formation discussions would be cancelled.

Well...the surface low has actually developed bouts of convective cloud tops today in intermittent small circular shapes just E of center. Meanwhile clouds west of center are suppressed by neighboring dry air mass S of Bermuda (see final paragraph of today's Open Atlantic waters disucssion for source of this dry air).

Despite looking more tropical with these intermittent convective bursts, the National Hurricane Center TAFB analyses keep handling it as a non-tropical entity. Yes they have downgraded the original cold front...which is now a long surface trough (red dashed line) E of 91-L in the above charts. But the surface trough attached to 91-L's center in yesterday's charts has been upgraded to a cold/occluded front in today's analyses from TAFB. 91-L has reached the warmest waters it will ever see as its track is now bending E and eventually N as it rounds the SE side of its parent upper low. Therefore if today's developments are not sufficient for the National Hurricane Center to declare subtropical cyclone formation, 91-L then is running out of time to become a subtropical cyclone.

What is causing 91-L to run out of time is approaching central US upper trough and surface front from Florida panhandle-North Carolina-Newfoundland seen in the above charts and mentioned in today's North America discussion below. This approaching frontal system is expected to absorb all vertical layers of 91-L beginning April 19 (tomorrow) into early on the 20th. I plan to issue a special update around lunchtime tomorrow cancelling these Atlantic birdseye discussions altogether until June 1 2012 (when Atlantic hurricane season officially starts). I am not yet cancelling these birdseye discussions tonight as I am on standby...waiting to see if the National Hurricane Center unexpectedly updates this system into a subtropical cyclone between now and lunchtime tomorrow.

...NORTH AMERICA DISCUSSION...A frontal system was newly-introduced to this discussion yeserday as it charged across the NW US with a 1012 mb low in NW North Dakota. With the support of its upper trough, this low has since deepened to 1003 mb over the W Great Lakes as shown in the above charts. Its supporting upper trough has merged with the central US upper trough also mentioned here yesterday. Cold front extends from the 1003 mb low to a new 1011 mb low over SE Colorado. The upper divergence supporting this 1011 mb low is a bit complicated. Based on the current state of 200 mb wind barbs, this low appears to have developed in split flow west of the two upper troughs just before they merged. The split flow was characterized by NW flow into the central US upper trough and W flow into the northern upper trough that has merged with the central US upper trough. Upper convergence west of the central US upper trough supports surface ridge centers of 1022 mb over east-central Mexico, 1023 mb at the Arkansas/Missouri border, and 1019 mb at the Dakotas.

Yesterday's 1007 mb cyclone near Maine is now over Newfoundland at 1015 mb. Yesterday it obtained its own supportive upper trough fragment that had split from the central US upper trough. This small upper trough is now over Ontario and Nova Scotia in the above charts. Upper convergence behind this upper trough supports surface ridge centers of 1027 mb over Ontario, 1026 mb near New York, and 1025 mb near N Virginia.

Lengthy cold front continues to extend from what is now the 1015 mb Newfoundland low to a 1016 mb low over North Carolina (was 1019 mb in yesterday's discussion) and 1013 mb low over the Florida panhandle (was 1018 mb over E Louisiana in yesterday's discussion). All of these surface features continue to receive supportive divergence from the central US upper trough.

...DISCUSSION OF OPEN ATLANTIC WATERS...Yesterday's discussion mentioned a 1001 mb cyclone over SE Greenland that today is still in the above charts at that location and now at 1002 mb. Yesterday's discussion also mentioned it was sharing supportive upper trough divergence with the 1007 mb cyclone near Maine (that is now 1015 mb over Newfoundland as remarked in today's North America discussion).

Extratropical (non-tropical) cyclone that made landfall in the British Isles mentioned yesterday is still clinging on to the scope of above charts as 1800Z TAFB still shows its tailing cold front over the N Canary Islands and Morocco. The upper trough associated with it has absorbed the E Atlantc cut-off upper low that was on its way to Morroco mentioned in yesterday's open Atlantic waters discussion. This absorption has resulted in a long upper trough axis in the far east in the above charts.

As predicted in detail during yesterday's open Atlantic waters discussion, the deep-layered ridge over the Azores has re-developed. It has a 1026 mb surface center in the above charts. Leftover E Atlantic upper ridge axis to the SW of the deep-layered ridge also persists with the continual support of warm air advection ahead of Invest 91-L.

Upper ridge that entered the W Atlantic yesterday is de-amplifying today. The west Atlantic 1024 mb surface ridge once supported by the eastern covnergence of the upper ridge remains stationary and has weakened further to 1022 mb. The de-amplification of the upper ridge and weakening of surface ridge is occuring as it becomes squeezed between low pressure features....including Invest 91-L to its east...the surface front extending from Florida Panhandle-North Carolina-Newfoundland in today's North America discussion...and the central US upper trough also in today's North America discussion. Yesterday's Caribbean/Gulf discussion mentioned sinking motion from these ridges creating a lot of dry air in the waters S of Bermuda. This dry air continues today as seen in the above thermodynamics chart.

Upper ridge over the Yucatan Peninsula has accelerated east and is now over Cuba and near Jamaica in the above charts. Divergence west of this upper ridge and east of the central US upper trough is increasing the moisture content and convective cloudiness in the western Caribbean region.

South American monsoon upper ridge shifted westward toward Central America yesterday, but has re-shifted back east over South America today.

A new shortwave upper trough is marked in the above charts just north of Panama, carved out in between the South America monsoon upper ridge and aformentioned upper ridge near Jamaica and Cuba.

...NORTH AMERICA DISCUSSION...A frontal system and associated upper trough, new to this discussion, is crossing the NW US after emerging from SW Canada. In the above charts, this frontal system is marked in the upper-left corner and has a 1012 mb surface low over NW North Dakota.

Vigorous 994 mb Great Lakes cyclone has moved into SE Canada, and now is weaker at 1007 mb while positioned just north of Maine in the above charts. As it continues racing eastward, the northern fragment of the supporting upper trough has fractured from the southern portion. Expect the northern portion of the upper trough to continue distancing itself from the southern portion while becoming associated with cold air advection just behind the 1007 mb cyclone racing eastward. Presently, upper convergence behind both upper trough portions is supporting a lengthy surface ridge across central North America with a 1026 mb center over eastern Hudson Bay, 1030 mb center over the Great Lakes, 1023 mb center over Colorado, and 1024 mb center in north-central Mexico.

Meanwhile, the southern portion of the upper trough remains strewn across the central US, and its eastern divergence is supporting a lengthy cold front extending from the aforementioned 1007 mb cyclone. The 1018 mb low along this cold front that was over E Texas 24 hours ago is now over E Louisiana. A new 1019 mb frontal low has developed over North Carolina.

Upper ridge over eastern US is no longer a North American feature as it gets pushed into the west Atlantic, but the upper ridge continues to amplify even further due to warm air advection ahead of aforementioned 1007 mb, 1019 mb, and 1018 mb frontal lows. The effect of this upper ridge on the Atlantic environment is covered later in today's Open Atlantic Waters Discussion below.

...DISCUSSION OF OPEN ATLANTIC WATERS...Yesterday's North America discussion mentioned a 992 mb cyclone emerging from Labrador, which is now over SE Greenland in the above charts at a weaker pressure of 1001 mb. The shortwave upper trough supporting it has been assimilated into the upper trough fragment supporting the 1007 mb cyclone near Maine mentioned in today's North America discussion. As a result, it now shares upper divergence support with the 1007 mb cyclone.

997 mb low heading from Greenland to British Isles mentioned yesterday has made landfall across the British Isles. Its center is now outside the scope of the TAFB and HPC analyses used in these discussions, so its central pressure value is not disucssed here today. However, TAFB analysis still includes this cyclone while showing its tailing cold front in the far NE Atlantic just N of the Azores.

Deep-layered ridge over the Azores is undergoing a complex evolution. Cool air advection/upper trough associated with the aformentioned British Isles cyclone has eroded the upper ridge center, and now only a surface 1031 mb center remains as marked in the above charts. Upper convergence behind the British Isle cyclone's upper trough presently supports the 1031 mb center. The eastern US upper ridge has been pushed into the W Atlantic as mentioned in today's North America discussion while still amplifying, resulting in a new upper-level high pressure E of Newfoundland and just NW of the 1031 mb center. Expect the new upper-level high to align over the 1031 mb center, resulting in the reformation of a deep-layered ridge near the Azores. Leftover central Atlantic upper ridge axis to the SW of the deep-layered ridge also persists, still supported by warm air advection ahead of developing subtropical cyclone E of Bermuda. The sprawling curvature of the fronts attached to the developing subtropical cyclone has shifted the warm air advection eastward, and as a result the upper ridge axis has also moved eastward into the E Atlantic.

E Atlantic cut-off upper low midway between Azores and Cape Verdes has accelerated eastward toward Morroco. This is because it has become pushed by the central Atlantic upper ridge axis which has been driven into the E Atlantic as described above.

The eastern US upper ridge has been pushed into the W Atlantic as mentioned in today's North America discussion while still amplifying. The west Atlantic 1028 mb surface ridge supported by the eastern covnergence of the upper ridge remains stationary and has weakened to 1024 mb. The weakening of the surface ridge is the result of it getting eroded by surrounding surface low pressure features, including the developing subtropical cyclone to its east and Louisiana-North Carolina-Maine frontal system to its west mentioned in today's North America discussion.

Hot topic today is aformentioned cut-off upper low vortex that formed E of Bermuda yesterday...and the subtropical cyclone formation its supporting at the surface. The surface low its supporting has weakened from 998 to 1002 mb as the surface low is now directly beneath the non-divergent upper low center, and the system as a whole is marked as a deep-layered cyclone in the above charts. With a lack of divergence at the upper low center, expect the 1002 mb surface low to continue weakening.

Yesterday's discussion mentioned how the thermodynamics had become less favorable for subtropical cyclone formation due to dry air ingestion and cold waters. The surface low (now 1002 mb) has made the W and SW turn toward warmer 20 to 21 deg C waters (predicted yesterday), but has not quiet yet made it to those waters. 24 hours ago, yesterday's discussion mentioned the surface low had just finished warding off dry air by wrapping in moist air induced by the upper low's divergence. The flow around the upper low's rim is no longer divergent, and so the moisture bands around the surface low have thinned when animating water vapor imagery over the last 24 hours. This may be allowing the rather dry air mass to its SW to re-penetrate into the circulation. As mentioned in yesterday's Gulf/Caribbean discussion, the source of this very dry air is upper convergence/surface divergence from east US upper ridge (now in the W Atlantic) and surface W Atlantic ridge.

To further complicate things, mixed messages are occuring with official meteorological agencies. This system has been upgraded to Invest 91-L by the Naval Research Laboratory (NRL), but the National Hurricane Center (NHC) TAFB analyses still show fronts attached to the surface low as if it is still non-tropical. The surface low has not quiet yet made it to the 20 to 21 deg C waters as remarked above. If persistent convective cloud tops do not develop when the surface low arrives at 20 to 21 deg C waters, this means the cut-off upper low above it is not cold enough to de-stablize the atmosphere at those water temps, and subtropical cyclone formation will no longer be possible. On the other hand if persistent convective cloud tops begin developing near the center, a special brief update will be issued on this blog declaring imminent risk of subtropical cyclone formation.

Yesterday's forecast delayed possible subtropical cyclone formation to as late as midday April 18 (tomorrow). Today's North America discussion mentioned a lenghty cold front from Louisiana-North Carolina-Maine and associated central US upper trough. Based on the frontal system's current eastward pace, the frontal system could begin absorbing all vertical layers of this potential subtropical cyclone beginning April 19 into early on the 20th. This timeframe marks the end of subtropical cyclone potential as it gets absorbed. It is possible I will be calling off subtropical cyclone potential sooner than those dates if persistent convective cloud tops do not develop when the surface low arrives at 20 to 21 deg C waters as remarked above.

...DISCUSSION OF GULF OF MEXICO AND CARIBBEAN SEA...Yesterday's east-to-west oriented shortwave upper trough over the Bahamas and just N of all the Caribbean islands has been absorbed by large upper low vortex over possibly developing subtropical cyclone.

Upper convergence southeast of the east US upper ridge (which has moved into the W Atlantic today), and surface divergence of the west Atlantic 1024 mb ridge continue to induce dry sinking air across the N Gulf and west Atlantic waters S of Bermuda. The dry air in the N Gulf is being replaced by moist air in a west-to-east fashion due to the arrival of 1018 mb frontal E Louisiana low (mentioned in today's North America discussion).

The E Lousiana 1018 mb low is supported by divergence ahead of central US upper trough (also mentioned in today's North America discussion) Divergence well-ahead of the central US upper trough also supports a new surface trough in the Bay of Campeche as marked in the above charts and as of 1800Z TAFB.

Upper ridge persists over the Yucatan peninsula of Mexico due to warm air advection ahead of aforementioned 1018 mb frontal low.

Shortwave upper trough that formed in central Caribbean (mentioned in yesterday's Gulf/Caribbean discussion) is being tugged slowly eastward by upper-level cyclonic flow associated with possibly developing subtropical cyclone to the NE.

As central Caribbean upper shortwave trough has dug eastward, the South American monsoon upper ridge to its south has been pinched away. This upper ridge is reforming westward more toward Central America and may merge with Yucatan Peninsula upper ridge mentioned above.

2012 Atlantic Hurricane Season Birdseye Discussion #5

...APRIL 16 2012...This discusion has been released much later than intended due to power outage at my residence. It has actually been released just after midnight into the first minutes of April 17 2012.

1013 mb frontal low east of Bermuda deepens to 998 mb, a rate of 15 mb over the previous 30 hours, while becoming well-organized. Subtropical cyclone possible in the next 36 hours.

This is the fifth birdseye discussion of the 2012 Atlantic Hurricane Season. See previous discussion #3 concerning the idea behind this new type of discussion forum.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1928Z-released HPC analysis.

...NORTH AMERICA DISCUSSION...The vigorous central US 989 mb cyclone that produced a severe weather risk across parts of Texas, Arkansas, Missouri, eastern Nebraska, and Minnesota has lifted NE into the Great Lakes region as a 994 mb cyclone as marked presently in the above charts. A summary of yesterday's severe weather produced by this 994 mb cyclone is provided in the final section of today's discussion. The equally vigorous upper trough supporting this cyclone follows behind while positioned across the central US. Cold front extends south from the 994 mb cyclone into eastern Texas, where a 1018 frontal mb low is present and also supported by divergence east of the central US upper trough. An upper convergent environment behind the central US upper trough is supporting a disorganized 1024 mb western US surface ridge.

Mexican monsoonal surface trough/low that is normally outside of the scope of the above charts has moved back out of scope (unlike 24 hours ago). Its barely visible in the above charts as a surface trough in east-central Mexico as of 1800Z TAFB.

Upper ridge over eastern US continues to amplify due to continued immense warm air advection ahead of aforementioned 994 mb cyclone presently over the Great Lakes. The amplification of this upper ridge has resulted in a variety of features in the west Atlantic Ocean which are covered later in today's Open Atlantic Waters Discussion below.

As predicted yesterday, 999 mb cyclone over the S tip of Husdson bay has intensified while moving east as it successfully advected in enough cold air behind it to carve a supporting shortwave upper trough which is now present over eastern Labrador. The 999 mb cyclone itself has moved rapidly offshore from Labrador and deepened to 992 mb as labeled in the above charts. Convergence behind the shortwave upper trough supporting 1020 mb ridge center over north-central Labrador.

...DISCUSSION OF OPEN ATLANTIC WATERS...985 mb cyclone near S Greenland has ejected east-northeast toward the British Isles of Europe as it weakens to 997 mb as shown in the above charts. The northern fragment of supporting west Atlantic upper trough has fractured away while moving with the 997 mb cyclone. The remaining southern fragment of the west Atlantic upper trough has evolved into a cut-off upper low supporting subtropical cyclone formation as has been forecasted by computer models for the last several days.

Deep-layered blocking ridge persists over the Azores...featuring presently an impressive 1036 mb surface center. The S Greenland cyclone is now passing north of the deep-layered ridge...thus it is unable to provide additional warm air advection to support the ridge's upper layers. Warm air advection is now being supplied by southerly flow ahead of developing subtropical cyclone east of Bermuda. Leftover central Atlantic upper ridge axis to the SW of the deep-layered ridge also persists, also supported by warm air advection ahead of developing subtropical cyclone.

Cut-off upper low persists in the far east Atlantic midway between Azores and Cape Verdes now drifting east toward Morroco. Divergence east of the cut-off upper low has been battling dry air that was once produced by what is now the deep-layered ridge over the Azores. The lift created by the upper low's eastern divergence has been successfully "moistening away" the dry air in the region when animating the thermodynamics charts over the last 72 hours. Satellite imagery shows no weather associated with the divergent region of the cut-off upper low, but the observed moistening may allow this to begin at some point.

Upper ridge over the eastern US continues to greatly amplify due to strong warm air advection ahead of aformentioned 994 mb cyclone over Great Lakes. The west Atlantic 1029 mb surface ridge supported by the eastern covnergence of the upper ridge remains stationary and is now at 1028 mb. The amplification of the east US upper ridge has allowed the southern fragment of west Atlantic upper trough to amplify into an upper low supporting subtropical cyclone formation east of Bermuda. Although not mentioned in yesterday's discussion, yesterday's charts showed that the amplification of the east US upper ridge carved out a shortwave upper trough located NW of Bermuda whose divergence supported a light convective mass north of Bermuda. This short-lived shortwave upper trough has been absorbed by the new cut-off upper low vortex E of Bermuda associated with subtropical cyclone development...while the convective mass itself has spun up into a weak 1022 mb low pressure swirl well-defined in visible satellite photos earlier today. This 1022 mb low is not tropical in nature...it got its support from the shortwave upper trough that has been absorbed and therefore it will soon dissipate or get absorbed into the developing subtropical cyclone E of Bermuda.

Hot topic today is aformentioned cut-off upper low vortex that formed E of Bermuda today...and the subtropical cyclone formation its supporting at the surface. The 1013 mb frontal low that formed 1200Z yesterday has intensified to gale force with 998 mb thanks to plenty of divergence east of the cut-off upper low. The 998 mb low has developed an occluded front, which is the first step to developing a low-level warm core for subtropical cyclone formation. It has also whirled NNW into a position beneath the cut-off upper low. The cut-off upper low center itself is non-divergent, but the 998 mb surface low may be allowed to deepen a bit more thanks to divergence caused by split flow between the north side of the upper low and west side of the Azores ridge. Albeit, this split flow divergence is north of the 998 mb center rather than above it, so it may/may not be helpful in deepening the 998 mb low further.

The NNW track and intensification of the 998 mb low has placed it at a thermodynamic disadvantage for subtropical development. Using today's thermodynamic chart, the NNW track has placed it over 19 deg C water, located betwen the 20 deg C isotherm to its south and another 20 deg C isotherm to its north associated with the Gulf Stream. It takes a very cold temp upper low to de-stabilize the atmosphere for convection to begin with water temps that cold. However, even if convection began, it would be cloudless convection at the center of circulation. This is because the 998 mb cyclone wrapped in a significant amount of dry air to its west while intensifying over the last 30 hours. The source of ths dry air is mentioned in yesterday's Caribbean/Gulf discussion...which mentioned the east US upper ridge/west Atlantic surface ridge produced sinking dry air that had spread the northern Gulf dry air mass into the Atlantic S of Bermuda.

Yesterday's discussion mentioned subtropical cyclone formation was not expected before the 17th (tomorrow)...which indeed has become true. The above paragraph suggests it may never happen. However, the NNW track of the 998 mb low is forecast to bend W and even SW as it continues clockwise beneath the cut-off upper low, which will take it away from the 19 deg C isotherm and back to 20 to 21 deg C waters. Water vapor imagery also shows the 998 mb cyclone has warded off the earlier-ingested dry air by wrapping in the moist air induced by the eastern divergence of the cut-off upper low. These factors place the 998 mb low increasingly back toward a more favorable thermodynamic picture.

What happens in the next hours is crucial. If convective cloud tops (with the newly-moistened air) do not develop when the 998 mb low arrives toward 20 to 21 deg C waters, this means the cut-off upper low above it is not cold enough to de-stablize the atmosphere at those water temps, and subtropical cyclone formation will no longer be possible. On the other hand if convective cloud tops begin developing near the center, a special brief update will be issued on this blog declaring imminent risk of subtropical cyclone formation. Given the thermodynamics were unfavorable over the prior 30 hours as discussed above...subtropical cyclone formation potential is now delayed and now possible in the next 36 hours as of this writing. This means it could be as late as midday April 18 before a subtropical cyclone forms.

...DISCUSSION OF GULF OF MEXICO AND CARIBBEAN SEA...East-to-west oriented shortwave upper trough in the Gulf of Mexico has been lodged SE into the Bahamas and just N of all the Caribbean islands due to amplifying east US upper ridge. Upper convergence north of this upper trough axis, upper convergence southeast of the east US upper ridge, and surface divergence of the west Atlantic 1028 mb ridge are all teaming for dry sinking air in the N Gulf and. west Atlantic waters S of Bermuda.

Northern South Amercian monsoon upper ridge continues to be choked by west Atlantic upper trough which has now amplified into upper low vortex supporting possible future subtropical cyclone.

New upper ridge amplifying over the Yucatan peninsula of Mexico due to warm air advection ahead of 1018 mb frontal low over E Texas mentioned in today's North America discussion.

A new shortwave upper trough has been carved out in the central Caribbean...in between the new shortwave upper ridge over the Yucatan and upper ridge associated with aformentioned South American monsoon.

...SUMMARY OF APRIL 15 2012 SEVERE WEATHER PRODUCED BY UNITED STATES CYCLONE...NOW CURRENTLY AT 994 MB OVER THE GREAT LAKES REGION OF NORTH AMERICA...(Supercell #1) Weak tornado near Ericson in NE Nebraska. The tornado dissipated, and then the supercell re-produced another brief tornado near the NE Nebraska/SE South Dakota border. The cell continued NE and produced yet another brief tornado in SW Minnesota well to the south of Hutchinson before dissipating.

(Supercell #2) New tornado-producing supercell in SW Minnesota to the east of supercell #1. Signature was just north of Glencoe and not far west of Minneapolis/St. Paul, and then tornado signature quickly dissipated.

(Supercell #3) New tornado warning around 6:21 PM CDT on a disorganized supercell heading ENE in direction of Batesville, Arkansas. The cell quickly became disorganized and elongated north-south by 6:38 PM CDT at a location west of Batesville.

(Supercell #4) Supercell explosively develops just SW of Victoria, Texas tracking ENE by 6:35 PM CDT. Supercell was well-organized with hook echo but not yet tornado warned. At 6:36 PM CDT...it received severe thunderstorm warning. The cell continues east with its hail core passing over Victoria by 7:32 PM CDT. The south end of the hail showed another tornadic-like hook just SE of Victoria at this time. The hook echo dissipated, and the supercell became less organized.

(Supercell #5) Just SW of Supercell #4...a new supercell erupted and also had a severe T-storm warning by 6:53 PM CDT. The cell was located just south of Goliad, TX. It later merged with the remnants of supercell #4.

...NORTH AMERICA DISCUSSION...The SW US surface cyclone reponsible for severe weather over western Oklahoma, Kansas, eastern Nebraska, and parts of Iowa yesterday has continued to deepen, and reached 989 mb at the Kansas/Nebraska border as shown in the above charts. The 989 mb cyclone is being supported by strong divergence ahead of the west US upper trough which has now moved into the eastern Rocky Mountains. Vigorous cool air advection behind the 989 mb cyclone in turn has amplified the western US upper trough, and the upper trough now features a vort max (upper low) over western Nebraska. This 989 mb cyclone continues to be dangerous today as it produces southerly flow pushing in low-level warmth/moisture, which collides with cooler upper westerly flow en route to east US upper ridge, favoring directional wind shear and instability for severe weather across Missouri, Iowa, Minnesota, and Arkansas where tornado watches have been in effect. A summary of yesterday's severe weather produced by this 989 mb cyclone is provided in the final section of today's discussion.

Upper divergence is present well SE of the west US upper trough supporting the 989 mb cyclone. Normally the Mexican monsoonal surface trough/low is outside of the scope of the above charts, but this upper divergence has allowed it to be displaced a bit east and be stronger, featuring a 1002 mb center just SW of Texas and a surface trough extending from that 1002 mb center all the way toward Central America.

Upper ridge which has moved into the eastern US yesterday has greatly amplified due to strong warm air advection ahead of aformentioned 989 mb cyclone. The 1029 mb surface ridge supported by the eastern covnergence of the upper ridge has shifted offshore into the west Atlantic and still remains at 1029 mb.

Mentioned briefly in yesterday's North America discussion was a 1005 mb cyclone just NW of Newfoundland, which has now been absorbed by strong cyclone S of Greenland. The cold front ushered in by the now-gone 1005 mb cyclone is strewn east-west across southern Canada and has overspread yesterday's 1001 mb cyclone over SW Ontario. This 1001 mb cyclone has slid east along the south Canada front and deepened to 999 mb while currently present over the southern tip of Hudson Bay in the above charts. Warm air advection ahead (cold air advection behind) the 999 mb cyclone will create a shortwave upper ridge east of it (upper trough west of it). In fact such an upper shortwave ridge is marked in the above charts over Labrador. In turn, divergence between the developing upper shortwave ridge and upper shortwave trough will cause the 999 mb cyclone to gradually strengthen while heading east along the front.

...DICUSSION OF OPEN ATLANTIC WATERS...High seas south of Greenland still dominated by intense surface cyclone currently at 985 mb, the same pressure it had 24 hours ago. The cyclone earlier bottomed-out at 962 mb, and is now weakening as the lengthy west Atlantic upper trough axis (offshore of east US) has neared it. This weakening is induced as the axis itself has less upper divergence than the environment east of the axis. Thus expect the cyclone to continue weakening through the next several hours.

Central Atlantic deep-layered ridging has been pushed toward east Atlantic ahead of S Greenland cyclone and its very long oceanic cold front. As predicted yesterday, the northern portion of the upper ridge has amplified into an upper high pressure center over the Azores thanks to continued warm air advection ahead of the S Greenland cyclone. The new upper high has vertically aligned with the strong surface ridge (presently 1032 mb) near the Azores, resulting in a blocking deep-layered high pressure over the Azores. To the southwest of the blocking high is a leftover central Atlantic upper ridge axis supported by continued warm air adection ahead of oceanic cold front extending from the S Greenland cyclone.

A surface trough is added from the Canary Islands to southern Morocco in the 1200Z NHC TAFB analysis (shown in the above charts as well). It appears that this trough is supported by divergence between upper northerlies east of the deep-layered Azores ridge and mainstream mid-latitude upper westerlies.

Cut-off upper low persists in the far east Atlantic midway between Azores and Cape Verdes. Divergence east of the cut-off upper low has been battling dry air that was once produced by what is now the deep-layered ridge over the Azores. The lift created by the upper low's eastern divergence has been successfully "moistening away" the dry air in the region when animating the thermodynamics charts over the last 48 hours. Satellite imagery shows no weather associated with the divergent region of the cut-off upper low, but the observed moistening may allow this to begin at some point. The divergent region of the cut-off upper low will however struggle to produce a surface trough while battling high surface pressures associated with the Azores deep-layered ridge.

1013 mb low has been added by 1200Z TAFB along the cold front extending from the S Greenland cyclone, located well east of Bermuda. The cyclone and lengthy cold front has been supported over the last days by a rather large west Atlantic upper trough offshore of east US. Yesterday's computer model runs suggested that the upper trough would split into a southern cut-off E of Bermuda and northern portion "running away" with S Greenland cyclone. However, this split is expected any time now. The cut-off upper trough E of Bermuda gets trapped between the above-discussed deep-layered Azores ridge and upper ridge over the eastern US mentioned in today's North American discussion. The models predicted the severe-weather producing west US cyclone would amplify the east US upper ridge (with warm air advection), and this indeed has begun over the last 24 hours. As the east US upper ridge continues amplification, this will allow the cut-off upper trough E of Bermuda to amplify into a rather impressive cut-off upper low vortex E of Bermuda by April 17. What is now the new 1013 mb frontal low will be present beneath the divergent east side of the cut-off upper low such that it flourishes eventually into a non-frontal subtropical cyclone. I do not expect subtropical cyclone formation before April 17 as the cold front across the 1013 mb low needs to decay into a non-frontal surface trough in order to classify the system as subtrpoical in the first place. The dissipation of air temperature contrasts across the front (to qualify it as non-frontal) is not an instantaneous process, and therefore no subtropical cyclone is expected before April 17.

The models show the subtropical cyclone making a clockwise loop E of Bermuda while steered by the cut-off upper low vortex from the 17th to 19th. Using today's thermodynamics chart, this keeps the forecasted subtropical cyclone well north of the 26 deg C isotherm, over waters between 20 to 22 deg C. This seems to be the only disadvantage to subtropical cyclogenesis. It is going to take a very cold-temperature upper low to produce instability and convection with surface water/air temps that mild. However, the cut-off upper low vortex E of Bermuda developed by the models seems impressive enough to be up to the challenge...stay tuned!

...DISCUSSION OF GULF OF MEXICO AND CARIBBEAN SEA...East-to-west oriented shortwave upper trough still present over the Gulf of Mexico based on latest 200 mb wind barbs in the above charts. Upper convergence north of this upper trough axis, upper convergence southeast of the east US upper ridge, and surface divergence of the west Atlantic 1029 mb ridge are all teaming up to expand the intensity of sinking, dry air across the northern Gulf. This dry air mass has spread into the west Atlantic waters S of Bermuda.

Northern South Amercian monsoon upper ridge continues to be choked by west Atlantic amplified upper trough offshore of US (located due north). Although there is some storm activity remaining with the monsoon, it is not as impressive as it was 72 hours ago.

...SUMMARY OF APRIL 14 2012 SEVERE WEATHER PRODUCED BY SW US CYCONE...NOW CURRENTLY AT 989 MB OVER THE CENTRAL US...The following preliminary summary is divided into thirteen convective supercell areas that developed during and after yesterday's discussion.

(Supercell #1) There was a supercell T-storm induced tornado in the late afternoon hours near Salina, Kansas.

(Supercell #2) Well SE of Dodge City, Kansas...a supercell T-storm produced a tornado tornado headed first toward Greensburg. It passed just 2 miles NW of Greensburg and was spotted by observers at night. The tornado then moved thru Fellsburg...heading toward Trousdale...Belpre, and then Macksville. A tornado emergency was issued for Macksville. Afterwards, the destructive tornado moving just north of Saint John and was about to head toward Hudson. After Hudson, the tornado headed toward Lyons & just N of Sterling but with a weaker radar signature. Affiliate KSN news (from Witchita, Kansas) reported power flashes at 10:03 PM CDT according to a storm chaser just west of Lyons.. signs that the tornado was regaining strength. KSN news reported power flashes in Lyons at 10:16 PM CDT. After clearing Lyons, the tornado headed toward rural grounds...but its long range track eventually threatened Salina and eventually Abilene, Kansas. A new tornado warning at 10:41 PM CDT was issued for this tornado just SSW of Salina. It was doing damage near Smolan, a town well south of Salina. The hail core NW of tornado center was hitting Salina at 11:00 PM CDT. Hail core then moves into Solomon (midway between Abilene and Salina) along I-70 at 11:18 PM CDT. The tornado signature was weakening on radar along I-70 at 11:18 PM CDT. Tornado signature collapses into multiple disorganized hooks along I-70 at Abeline & Solomon, which indicated tornado dissipation by 11:24 PM CDT. Tornado re-established itself by 11:32 PM CDT at a position just north of Abeline. Sloppy tornado signatures north of Chapman & Abeline at 11:35 PM CDT. Not long after...the tornado warnings with this supercell were finally cancelled.

(Supercell #3) A supercell T-storm in east Reno County Kansas (Hutchinson area) produced a tornado...and was heading NE toward Hillsboro and passing NW of Marion. Later, radar suggested it passed south of Herington. At 9:22 PM CDT...tornado was 4 miles north of Wilsey moving NE in east-central Kansas. At 9:35 PM CDT...radar image posted showing weaker/dissipating tornado signature that was passing northwest of Council Grove and east of Herington.

(Supercell #4) A vigorous supercell T-storm produced a new tornado starting near Woodward, OK during the late afternoon. Shortly thereafter, it passed by Waynoka, Dacoma, and then later moved toward Manchseter area of Oklahoma. On its way toward Manchester, affiliate News9 aired dramatic footage including an explosion of a gas tank & multiple vortices. Before heading toward Manchester, OK, it passed just N of Byron. After passing just NW of Manchester, it moved across Oklahoma border into south-central Kansas. It is making a bee-line to southern Witchita, KS. On its way toward Witchita...it produced an extremely impressive velocity doppler signature south of Argonia. At 9:33 PM CDT...velocity doppler signature was closing in on Conway Springs and Belle Plaine with bee-line still toward Witchita. It was at this time affiliate KSN reported the sounding of tornado sirens in Witchita. At 10:00 PM CDT...two circulations were spotted on radar heading into Clearwater & Conway Springs as the supercell neared Witchita. AT 10:13 PM CDT...the tornado re-established itself as a single circulation just NE of Clearwater and heading NNE to downtown Witchita. SW Witchita reported powerflashes at 10:15 PM CDT according to KSN. A tornado emergency was issued for Witchita...the largest tornado emergency issued during the evening considering the population of the area. KSN reported reported power outages in SW Witchita at 10:22 PM CDT. At 10:24 PM CDT...tornado spotted on I-35 turnpike with the apperance of a dangerous wedge. The tornado banked NE at 10:29 PM CDT such that it will move through SE Witchita and along the I-35 turnpike. Along the turnkpike, the tornado moving NE toward Andover by 10:39 PM CDT. Next was Towanda and El Dorado, Kansas by 10:42 PM CDT. Radar showed the tornado signature on top of El Dorado at 11:00 PM CDT. AT 11:20 PM CDT, the tornado signature was parelleing I-35 moving NE en-route to pass south of Cassoday & into rural areas of NW Greenwood county, then rural SE Chase County, and then a tornado warning was issued in southern Lyon County by 11:50 PM CDT. By midnight thru 12:12 AM CDT, the storm looked disorganized in S Lyon county and south of Emporia. Its tornado warning was finally dropped by 12:30 AM CDT, making it the longest-track tornado of the event.

(Supercell #5) Large T-storm cluster with bow echo was seen in Iowa with radar. Frequent rotation within the bow echo near Des Moines...however bow echo continues east with no tornado warnings ever issued.

(Supercell #6) A supercell in northern Oklahoma put down tornado near Alva/Cherokee eventually taking a track toward Witchita, Kansas. This circulation was overtaken by the tornado that crossed the border from Manchester, OK (supercell #4) before it had a chance to get to Witchita, and it was suprecell #4 as discussed above that would eventually hit Witchita.

(Supercell #7) Severe T-storm with hook echo south of Hastings, Nebraska just before 10:00 PM CDT. This T-storm cluster produced a tornado warning just north of Lincoln, Nebraska by 11:42 PM CDT. This storm loses tornado warning by 12:03 AM CDT while en-route to pass just south of Omaha, Nebraska. Again it gets tornado warned from 12:40 to 1:09 AM CDT as it crosses the Nebraska border just E of Omaha into west-central Iowa & just west of Atlantic, Iowa. This final tornado warning was brief and tornado signature was disorganized.

(Supercell #8) Off the west side of supercell #2...new tornado warning for Geneseo, Kansas at 10:53 PM CDT. The new circulation was east of Claflin and west of Geneseo heading to Geneseo. Later at 10:59 PM CDT, Lorraine just NW of Geneseo under a potential tornado touchdown with tornadic circulation wraped in heavy rain according to radar. At 11:10 PM CDT...Geneseo was spared as the tornado passed north of the city and was heading ENE. At 11:20 PM CDT...the tornado was now heading toward the Salina area. Brookville, Bavaria, and Salina were on its path at 11:31 PM CDT...& KSN reported NCAR had spoted the torando. By 11:59 PM CDT...circulation moving into Salina but less organized on radar. Warning was cancelled shorlty after midnight local time.

(Supercell #9) New tornado warning at 12:03 AM CDT just SE of Metador in north-central Texas. Tornado warning was short-lived

(Suprecell #10) New tornado warning at 12:03 AM CDT just SE of Gage, Oklahoma heading toward Woodward, Oklahoma. This new tornado was en-route to work its way toward Alva near where supercell #6 went. By 12:19 AM CDT, the tornado was moving into the Woodward area. By 12:29 AM CDT...the tornado signature dangerously directly on top of Woodward, OK. By 1:14 AM CDT, tornado signature appears to be passing well NW of Alva. The dissipating tornado crosses the Oklahoma border into just S of Medicine Lodge, KS by 1:39 AM CDT. Reports the following morning indicated five fatalities due to the direct strike of this tornado upon Woodward.

(Suprecell #11) New tornado warning around 12:18 AM CDT near Elk City, OK tracking ENE eventually en route to pass just north of Clinton, OK. Tornado warning gone by 12:34 AM CDT as it becomes indistinct within nearby squall line. Tornado warning re-issued on it by 12:45 AM CDT as it is slated to pass well north of Clinton. Once again loses tornado warning and re-assimilates into the squall line by 1:39 AM CDT.

(Supercell #12) Major rapid devlelopment of hook echo passing thru Wakefield, Kansas, and a tornado warning by 12:54 AM CDT. This is remnants of supercell #8. Eventually this impressive tornado signature passed just north of Manhattan, Kansas. By 1:34 AM CDT...it still has impressive radar bean-shaped signature while sliding ENE between Manhattan and Marysville. Minutes later, tornado signature much less impressive and dissipating.

(Supercell #13) New tornado warning just southeast of Medicine Lodge, KS passing thru the SE half of that city and tracking NE. Tornado warning SE of Medicine lodge is removed by 1:11 AM CDT.

2012 Atlantic Hurricane Season Birdseye Discussion #3

...APRIL 14 2012...This is the third "birdseye" discussion of the 2012 Atlantic Hurricane Season. I conceived the idea of analyzing the entire Atlantic basin from two maps that provide a "birdseye" view of the region. I found this method useful for understanding the day-to-day evolution of the Atlantic basin throughout Hurricane Season 2011.

Atlantic Hurricane Season does not start until June 1. However, this discussion is issued due to persistent computer model support for subtropical cyclone formation in the central Atlantic during the next days.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1200Z, and the 1330Z-released HPC analysis.

...NORTH AMERICA DISCUSSION...System over the western United States continues to become more complex in last 48 hours. Aloft, the system is anchored by west US upper trough still stationary over the eastern borders of California and Nevada. The vigorous surface cyclone (with multiple pressure centers below 1000 mb) that the west US upper trough supported has ejected northward into SW Ontario and weakened to 1001 mb. As it ejected, local cool air advection on its west side has supported the formation of small upper low vortex over SE Manitoba. The central US upper ridge supported by warm air advection east of the 1001 mb cyclone has shifted into the eastern US overnight. This 1001 mb cyclone produced a severe weather convective mass over Oklahoma last evening that has since moved ENE into Missouri and Ohio valley, a position beneath the east US upper ridge. This convective mass is now embedded in a lower shear environment among deep-layered westerlies in the east US upper ridge and SE of the 1001 mb cyclone. The reduction in shear across the convective mass means that is a lower risk of severe weather, but still has embedded thunderstorms.

The west US upper trough no longer supports the SW Ontario 1001 mb cyclone. The 1001 mb cyclone is now being supported by divergence between the SE Manitoba upper low and east US upper ridge. The west US upper trough instead supports another vigorous surface cyclone with multiple pressure centers below 1000 mb that has rolled in from California overnight. This SW US surface cyclone, new to this discussion, has a 990 mb center over Colorado and 995 mb center over SW Utah in the above charts. This SW US surface cyclone is extremely dangerous today as it produces southerly flow pushing in low-level warmth/moisture, which collides with cooler upper westerly flow en route to the east US upper ridge, favoring directional wind shear and instability for an extreme severe weather event across Oklahoma, Kansas, Nebraska, parts of Iowa, and parts of Missouri. Convective cloud tops on satellite and supercell T-storm signatures on radar are rapidly flourishing throughout the day, and residents in this area are urged to listen to local media for this dangerous severe weather event.

As discussed above, central US upper ridge has been pushed into east US by the 1001 mb surface cyclone in SW Ontario. As a result, the surface ridge supported by the convergent east side of the upper ridge has also shifted east. This surface ridge now has a single 1029 mb center just offshore of Cape Lookout, North Carolina.

Mentioned briefly in yesterday's discussion was a N Quebec 1008 mb cyclone that has marched across Hudson Bay. Since then, the cyclone has continued an ESE march and depeened to 1005 mb just NW of Newfoundland. Its associated shortwave upper trough has merged with prominent upper trough offshore of east US, and its western convergent side is supporting a 1019 mb surface ridge currently over the southern Hudson Bay.

...DISCUSSION OF OPEN ATLANTIC WATERS... High seas south of Greenland dominated by rapidly intensifying surface cyclone moving quickly NNE from Newfoundland. Yesterday's discussion mentioned this cyclone at 1003 mb and that it had stopped intensifying as it moved beneath a non-divergent upper low along the upper trough offshore of east US. Since then, the upper low has been absorbed by shortwave upper trough associated with above-discussed 1005 mb cyclone from N Quebec. Moreover, this shortwave upper trough has merged with the large upper trough offshore of east US, and in turn mass divergence east of the large upper trough has caused explosive intensification of yesterday's 1003 mb cyclone which has now rapdily deepeend to 985 mb as of the 1330Z HPC analysis. Expect the neighboring 1005 mb cyclone from N Quebec to become absorbed by the rapidly deepening 985 mb cyclone. This rapidly deepening cyclone will cause rough weather in the high seas south of Greenland as well as land areas of south Greenland.

Extending south of rapidly intensifying cyclone S of Greenland is a long cold front that has been attached to the cyclone, and also has been an area of interest for future subtropical cyclone formation. Yesterday's discussion of the cold front mentioned a 1008 mb low that formed east of Bermuda, but since then the 1008 mb low has been assimilated into the growing low pressure field of rapidly deepening cyclone S of Greenland. Further south, the cold front has pushed into the Dominican Republic and Puerto Rico and absorbed the non-frontal surface trough that was located north of Puerto Rico 24 hours ago.

Central Atlantic deep-layered ridging has been pushed toward east Atlantic ahead of rapidly deepneing cyclone S of Greenland and its very long oceanic cold front. The southern portion of the upper ridge has stopped amplifying, but the northern portion of the upper ridge is about to amplify further into an upper high located over the Azores due to the intense warm air advection ahead of deepning cyclone S of Greenland. Northerly convergent flow east of the amplifying upper ridge continues to support the strong surface ridge near the Azores which today is at 1031 mb. Expect the developing upper high and 1031 mb surface center to become aligned, which will result in an impressive blocking deep-layered high pressure centered over the Azores.

Computer model runs continue to support subtropical cyclone formation along the oceanic cold front extending from the deepening cyclone S of Greenland. The associated upper trough has been offshore of east US. This morning's GFS model run shows the southern portion of the upper trough becoming cut-off to E of Bermuda tomorow while the northern portion splits away to the NE while "running away" with the deepening cyclone S of Greenland. The cut-off upper trough E of Bermuda gets trapped between the above-discussed blocking Azores ridge and upper ridge over the eastern US mentioned in today's North American discussion. Warm air advection ahead of SW US surface cyclone (producing today's central US severe weather) will amplify the eastern US upper ridge such that the cut-off upper trough E of Bermuda also amplifies into a rather impressive cut-off upper low vortex E of Bermuda by April 17. Whatever is left of the oceanic cold front beneath the east side of the upper low vortex is progged by the models to spin up into a non-frontal subtropical cyclone supported by divergence from the cut-off upper low vortex, the process beginning on April 17.

The models show the subtropical cyclone making a clockwise loop E of Bermuda while steered by the cut-off upper low vortex from the 17th to 19th. Using today's thermodynamics chart, this keeps the forecasted subtropical cyclone well north of the 26 deg C isotherm, over waters between 20 to 22 deg C. It is going to take a very cold-temperature upper low to produce instability and convection with surface water/air temps that mild. The cut-off upper low vortex E of Bermuda developed by the models seems impressive enough to be up to the challenge, so subtropial cyclone formation is still possible...stay tuned!

As forecated in yesterday's discussion, the upper trough in the far east Atlantic has amplified into a cut-off upper low midway between the Cape Verdes and and Azores. The remainder of the upper trough has split off and is pushing toward western Europe, and its eastern divergent has begun to support the weak NE Atlantic extratropical surface low seen in visible satellite yesterday (and also briefly mentioned yesterday). This weak NE Atlantic low had made landfall in west Europe, its tail end showing as a surface trough in today's 1200Z analysis from TAFB. Meanwhile, the divergent east side of the new cut-off upper low (between the Cape Verdes and Azores) has been fighting dry/sinking air that was earlier induced by the deep-layered ridge now developing over the Azores. Water vapor satellite imagery shows the air has moistened over the Cape Verdes, and so the divergent east side of the cut-off upper low may begin to produce some light weather.

...DISCUSSION OF GULF OF MEXICO...CARIBBEAN SEA...AND FLORIDA... Although present, a shortwave upper trough that formed over the SE US (Virginia, Carolinas, and Georgia) was not mentioned yesterday. This shortwave formed yesterday on the west flank of the larger upper trough off of the east US, and was carved out by the amplifying central US upper ridge which has since moved into the eastern US.

As the eastern US upper ridge has moved in, the SE US shortwave upper trough has been pushed southward into the Gulf of Mexico and Florida. Convergence south of the east US upper ridge and north of the Gulf shortwave upper trough is leading to sinking, dry air across the northern Gulf seen in today's thermodynamics chart. Divergence south of the Gulf shortwave upper trough is leading to a batch of moistening air seen over the Yucatan and western Caribbean Sea, but there is not much active weather with this moistening air.

It appears Northern South Amercian monsoon upper ridge continues to be a bit choked by the amplified upper trough near the east US (located due north). Although there is some storm activity remaining with the monsoon, it is not as impressive as it was 48 hours ago.

2012 Atlantic Hurricane Season "Birsdeye" Discussion #2

...APRIL 13 2012...This is the second "birdseye" discussion of the 2012 Atlantic Hurricane Season. I conceived the idea of analyzing the entire Atlantic basin from two maps that provide a "birdseye" view of the region. I found this method useful for understanding the day-to-day evolution of the Atlantic basin throughout Hurricane Season 2011.

Atlantic Hurricane Season does not start until June 1. However, this discussion is issued due to persistent computer model support for subtropical cyclone formation in the central Atlantic during the next days.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1200Z, and the 1330Z-released HPC analysis.

...WEST-TO-EAST DISCUSSION...Today's discussion will propagate from the west to east while referring to the above two birdseye charts.

System over the western United States has become more complex in last 24 hours. Aloft, the system is anchored by an upper trough axis currently positioned along the eastern borders of California and Nevada that has become stationary and more amplified. The vigorous 993 mb surface cyclone it supported yesterday has broadened into multiple pressure centers below 1000 mb, including the 999 mb center marked in the atmospheric features chart in northern Nebraska. The vigor and expanse of this surface cyclone has created mass cool air advection on its west side that is repsonsible for the amplifcation of the west US upper trough. Of note, low-level southerly flow east of the vigorous surface cyclone is driving warmth and moisture from the south, which collides with cooler westerly flow aloft favoring instability and directional wind shear for continued severe weather across portions of the central US.

Central US upper ridge axis has amplified over the last 24 hours, and expect it to remain amplified over the next days as warm air advection ahead of aforementioned vigorous west US surface cyclone continues. Central US upper ridge continues to support surface ridge with its eastern convergence. The surface ridge centers have shifted east into a 1024 mb center over SE North Carolina, and 1026 to 1027 mb center over southern Ontario and western New York.

As predicted during yesterday's discussion, upper trough/low near the eastern US has become further amplified in part by equal amplification of upstream central US ridge (driven by warm air advection ahead of west US cyclone), and by amplification of upstream Quebec upper shortwave ridge (driven by warm air advection ahead of 1008 mb cyclone that has moved across Hudson Bay into northern Quebec). The upper low along the upper trough axis has moved toward Newfoundland, and so has the 1004 mb cyclone it supported yesterday which has deepened only slighlty to 1003 mb as it moves into a less divergent environment beneath the upper low.

Expect the above-discussed amplification pattern of the upper trough/low near the eastern US to continue, which could allow subtropical cyclone formation along the cold front extending from the 1003 mb cyclone. The amplification process will be essential in this development as it will reduce the westerly vertical shear currently over the surface cold front. Thermodynamics are a disadvantage for development as this system will stay north of the 26 deg C SST isotherm. However the resulting amplification of the upper trough/low could lead to a large-scale upper low over the surface front whose cold temperature could allow for instability despite the mild water temps.

A non-frontal surface trough located just north of the Dominican Republic yesterday is present just north of Puerto Rico today. The surface trough is also supported by divergence ahead of the amplifying upper trough/low near the eastern US. However, the cold front extending from the 1003 mb cyclone should absorb it, shifting the potential for subtropical cyclone development to be somewhere along the cold front. Also getting help from the eastern divergence of the amplfiying upper trough/low near the east US is a new 1008 mb center along the cold front and east of Bermuda, over water temps of 20 to 21 deg C. It is not clear if this 1008 mb center could emerge as the subtropical feature of interest, but an increase in instability from present is certainly needed with those water temps. Amplification of the upper trough/low could lead to a large-scale upper low aloft whose cold temperature could allow for that instability and also a reduction of the immense westerly vertical shear in the area.

It appears Northern South Amercian monsoon upper ridge has been a bit choked by the amplifying upper trough/low near the east US (due north). Animating the 200 mb wind barbs over the last day suggests the amplificaiton of the upper trough/low has compressed the monsoon upper ridge a bit southward. If this is the case, the reduction of outflow from this upper ridge has calmed the thunderstorm intensity, and also this has resulted in the surface monsoonal 1012 mb low over north Colombia (present 24 hrs ago) to dissipate.

Central Atlantic still domianted by deep-layered ridging. The upper ridge axis in the area has greatly amplified due to continued warm air advection ahead of above-mentioned 1003 mb Newfoundland cyclone, and also warm air advection ahead of newly-formed 1008 mb cyclone east of Bermuda also mentioned above. Weak shortwave upper trough in the north-central Atlantic that was embedded in the upper ridge has contineud east to a position just south of the Azores today. Strong upper convergence east of the upper ridge axis and west of shortwave upper trough axis supports a continued 1032 mb surface ridge SW of the Azores. The convergence east of the upper ridge axis and surface divergence of the 1032 mb ridge is resulting in a large swath of sinking, dry air (seen in the above thermodynamics chart) and hence stable weather across the eastern Atlantic.

Mentioned breifly in yesterday's discussion was a 1006 to 1008 mb disorganized cyclone near south Greenland and beneath the north side of the above-mentioned central Atlantic upper ridge. Visible satellite suggests the eastern 1008 mb center is skirting ESE toward west Europe under the WNW flow from the central Atlantic upper ridge. Western 1006 mb center has weakened to 1012 mb and stationary near south Greenland. This has been a decaying system with no supportive divergence to be found at the north crest of the upper ridge axis.

In the far east Atlantic, yesterday's upper trough near the Cape Verde and Canary Islands has becoem further amplified and its postion has retrograded slighlty westward. The amplfication/retrogression of this upper trough is in part due ot the equal amplifcation of the upstream central Atlantic upper ridge discussed above. 200 mb wind barbs suggest a vort max developing midway between the Cape Verdes and Azores, suggesting that a cut-off upper low is expected to form at that location along the amplifying upper trough. Even though such an upper low will support divergence on its east side, abudandtly dry air generated by the neighboring central Atlantic ridge (also discussed above) will prevent active weather with this system.

2012 Atlantic Hurricane Season "Birsdeye" Discussion #1

...APRIL 12 2012...This is the first "birdseye" discussion of the 2012 Atlantic Hurricane Season, and also my first ever. I conceived the idea of analyzing the entire Atlantic basin from two maps that provide a "birdseye" view of the region. I found this method useful for understanding the day-to-day evolution of the Atlantic basin throughout Hurricane Season 2011.

Atlantic Hurricane Season does not start until June 1. However, this discussion is issued due to persistent computer model support for subtropical cyclone formation in the central Atlantic during the next days.

...ATMOSPHERIC FEATURES BIRDSEYE CHART... This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1200Z, and the 1329Z-released HPC analysis.

...WEST-TO-EAST DISCUSSION...Today's discussion will propagate from the west to east while referring to the above two birdseye charts.

Over the western United States is an upper trough axis currently positioned along the eastern borders of California and Nevada based on the lastest 200 mb wind barbs. Mass divergence east of the upper trough supports a surface non-tropical system, anchored by a 993 mb low at the Montana/Wyoming border and 1006 mb low in south-central New Mexico. Expect the 993 mb low to continue east and be the dominant feature of this non-tropical system, and maintain strength as it is currently well-within the eastern divergence of the west US upper trough. Of note, low-level southerly flow east of the 993 mb low and west of a 1028 mb Kentucky surface ridge is driving warmth and moisture from the south, which collides with cooler westerly flow aloft favoring instability and directional wind shear for severe weather across portions of the central US.

Continuing east, next major weather feature in the birdseye charts is a central US upper ridge. This upper ridge is supported by building warm air from the south courtesy of the flow ahead of the aforementioned 993 mb non-trpoical cyclone. Convergence east of the upper ridge axis supports a surface ridge axis that contains a 1028 mb center over Kentucky, 1027 mb center over NE Ontario, and 1026 mb center over NE Quebec.

Just off the eastern US is a major upper trough supporting an 1004 mb non-tropical cyclone that has just become occluded offshore of Nova Scotia. A brand new upper low has formed on the upper trough axis (east of Massachusetts) due to locally intense cool air advection behind the 1004 mb cyclone. Further amplification of the upper trough/low near the eastern US could be supported by amplification of upstream central US ridge (driven by warm air advection ahead of 993 mb cyclone), and by amplification of upstream west Quebec upper shortwave ridge (driven by warm air advection ahead of cyclone moving across Hudson bay). As this upper trough/low near the east US continues eastward and amplifies, it could support subtropical cyclone formation along the cold front extending from the 1004 mb cyclone...stay tuned! The amplification process will be essential in this development as it will reduce the westerly vertical shear currently over the surface cold front. Thermodynamics are a disadvantage for development as this system will stay north of the 26 deg C SST isotherm. However the resulting amplification of the east US upper trough/low could lead to a large-scale upper low over the surface front whose cold temperature could allow for instability despite the mild water temps.

A non-frontal surface trough is located just north of the Dominican Republic, and marked as the potential candidate for eventual subtropical cyclone formation in the above birdseye charts. The surface trough is also supported by the upper trough/low near the eastern US. Surface convergence from this trough and 1004 mb cyclone cold front, coupled with upper divergence ahead of the upper trough/low has produced a marked increase in convective cloudiness across the central Atlantic over the last 24 hours. Expect both the surface trough and 1004 mb cyclone cold front to supply the low-level vorticity of the possible subtropical cyclone in the next days.

Central Atlantic domianted by deep-layered ridge. The upper ridge axis is the result of warm air advection ahead of the aformentioned 1004 mb cyclone frontal system. In the midst of the upper ridge is a weak shortwave upper trough in the north-central Atlantic. At the north end of the upper ridge axis is a disorganized 1006 to 1008 mb non-tropical cyclone near southern Greenland. Mass convergence east of the upper ridge axis supports a large and intense 1032 mb surface ridge anchored southwest of the Azores. The convergence east of the upper ridge axis and divergence of the 1032 mb ridge is resulting in a large swath of sinking, dry air (seen in the above thermodynamics chart) and hence stable weather across the eastern Atlantic.

Finally, the easternmost feature in the above birdseye charts is an upper trough approaching west Africa and Europe from the Cape Verde and Canary Islands. Divergence east of this upper trough supports a surface cold front currently pushing into western Europe.